Overcurrent protection circuits are generally known—in particular in the form of circuit breakers.
Circuit breakers generally have a thermal overload release and an electromagnetic quick-action release. If the current flowing through the circuit breaker slightly exceeds a rated current, tripping takes place with a time delay, by way of the thermal overload release. In the event of a short circuit, in contrast, when the current rises rapidly, the electromagnetic quick-action release trips the circuit breaker with virtually no delay. The tripping of the circuit breaker has two effects. First, the circuit is opened directly. Secondly, a switching mechanism is tripped, so that the circuit is not closed automatically again once the circuit breaker has tripped.
Despite tripping with virtually no delay, the electromagnetic release does have a reaction time. During the reaction time, the load current rises above the identification current at which the electromagnetic release trips. This results in a large amount of wear due to contact erosion in the contact that is to be opened. If the current rises too rapidly, a continuous arc may result. Such a continuous arc is difficult to quench, and a failure to do so may lead to the complete destruction of the circuit breaker. Furthermore, such a continuous arc may make it impossible to switch off the current.